Rotary potentiometer

ABSTRACT

The resistance element of a potentiometer is a flat semicircular strip with ends having outward extensions providing jutting contact tabs that may be slipped into spring clips and inward extensions fitting into notches in a centering boss of the carrier plate of the device so that the resistance element can be accurately positioned without affixation. The rotating wiper is mounted on the inside surface of a drive wheel that has one contact that slides along the resistance element and a pair of spring contacts that engage an annular surface of a contact lug that passes under the resistance element in a channel in the carrier plate. The outer surface of the drive wheel has a spiral groove that guides a pointer. The axis of the drive wheel and of the potentiometer is skewed relative to the position of the thumb wheel by which the drive wheel is propelled, so that the spiral ridge on the thumb wheel will engage the crown teeth of the drive wheel at only one location. If the thumb wheel is made to project through a slot in a panel, the pointer will move essentially across the slot along or near the thumb wheel.

United States Patent [1 1 Koch et al.

ROTARY POTENTIOMETER lnventors: Dieter Koch, Escherde; Peter-Josef Graf,Hildesheim, both of Germany Assignee: Blaupunkt-Werke GmbH,

Hildesheim, Germany Filed: Jan. 24, 1974' Appl. No.: 436,209

30 Foreign Application Priority Data 'Feb. 16, 1973 Germany 2307680 US.Cl 338/162, 338/163, 338/174,

338/196, 338/202, 338/D1G. 1 Int. Cl. H0ll 9/02 Field of Search 338/162,.174, 196, 202,

338/118, 160, DIG. l, 334, 166,168,175,

[56] References Cited UNITED STATES PATENTS [451 Mar. 18, 1975 PrimaryExaminerBruce A. Reynolds Attorney, Agent, or Firm-Flynn & Frishauf [57]ABSTRACT The resistance element of a potentiometer is a flatsemicircular strip with ends having outward extensions providing juttingcontact tabs that may be slipped into spring clips and inward extensionsfitting into notches in a centering boss of the carrier plate of thedevice so that the resistance element can be accurately positionedwithout affixation. The rotating wiper is mounted on the inside surfaceof a drive wheel that has one contact that slides along the resistanceelement and a pair of spring contacts that engage an annular surface ofa contact lug that passes under the resistance element in a channel inthe carrier plate. The

outer surface of the drive wheel has a spiral groove that guides apointer. The axis of the drive wheel and of the potentiometer is skewedrelative to the position of the thumb wheel by which the drive wheel ispropelled, so that the spiral ridge on the thumb wheel will engage thecrown teeth of the drive wheel at only one location. If the thumb wheelis made i to project through a slot in a panel, the pointer will moveessentially across the slot along or near the thumb wheel.

4 Claims, 5 Drawing Figures r 1 ROTARY POTENTIOMETER The inventionrelates to a rotary potentiometer, particularly of the kind that is usedfor making adjustments on a television set, in which a control wheel isin the form of a knurled disc of which only a little of the peripheryprojects through the front of the set and in which a rough indication ofthe adjustment is provided by a pointer which, like the control wheel,moves in a plane perpendicular to the panel of the set through which thecontrol wheel protrudes. This invention relates to the electricalelements of such a potentiometer.

The type of mechanical control drive for a potentiometer just mentionedis described in the published German Patent application(Offenlegungsschrift) No.

1,951,972. In this type of device one entire revolution of the controlwheel advances a crown toothed drive wheel affixed to the potentiometershaft by only one tooth. This mechanical drive system is furtherdescribed below so that the cooperation of these mechanical elements andof the electrical elements constituted according to this invention maybe fully appreciated. In a known form of potentiometer driven by amechanical drive of the type just mentioned, the resistance elementalong which the contact of the wiper arm moves when the potentiometer isadjusted is riveted at its connections with connection lugs, the rivetsholding the resistance element and its lugs to the carrier plate of thedevice. This way of providing for connection to the resistance elementis produced with considerable variation in the resistance of theconnection, which is dependent upon the stability of the resistancecarrier material, the surface of the material and the clamping force ofthe riveting. Furthermore, the riveting can produce cracks in thecarrier material and in the layers applied to it. When connections aresoldered to the lugs, furthermore, there is also the risk that aninsulating layer will be deposited between the resistance layer of theresistance element and the slider of the potentiometer, as the result ofcondensation of soldering vapors.

It is an object of the invention to reconstitute the electrical elementsof this type of potentiometer so as to overeome the above mentioneddisadvantages.

SUBJECT MATTER OF THE PRESENT INVENTION Briefly, the resistance elementis made in the form of a semicircular flat piece with extendedlengthshaving outwardly extending portions providing connection tabs withmetallized surfaces extending beyond the edges of the carrier plate. Acentering boss on the carrier plate fits against the interior edge ofthe resistance element and provides notches into which inwardprojections provided on the resistance element nest. The resistanceelement is seated on the carrier plate in a plane parallel to the discof its drive wheel, which is skewed at a small angle with reference tothe plane of the disc of the control wheel.

The advantages of this arrangement are that the connection tabs of thepotentiometer are readily and conveniently insertable in spring contactdevices and it is relatively simple as well as reliable to mount one ormore such potentiometers in spring clips.

The invention will be further described by way of example with referenceto the accompanying drawings in which:

FIG. 1 is a plan view ofa partly assembled potentiometer;

FIG. 2 is a plan view of a completely assembled potentiometer;

FIG. 3 is an elevation view from the front side of the potentiometer ofFIG. 2, which is at the top in FIG. 2;

FIG. 4 is a plan view of the drive wheel of the potentiometer of FIG. 2,shown from the side carrying the contact wiper or slider of thepotentiometer, and

FIG. 5 is a plan view of a modified form of resistance element for usein the potentiometer of FIGS. 1, 2 and 3.

FIG. 1 shows a carrier plate 1 on which have been mounted the controlwheel 2, the resistance element 21 and the central connection lug 23.The control wheel 2 is mounted on the carrier plate 1 by means of a hub30 surrounding the cylindrical post 3 which is molded integral with thecarrier plate. Either or both of the ends of the hub 30 may be split, asshown for example at 31, to assure a good rotating'fit.

FIG. 2 shows the potentiometer of FIG. 1 after the drive wheel 7- andthe pointer 13 have been put into place. FIG. 3 is an edge view of theassembly of FIG. 2 from the front edge of the device, which is at thetop in FIG. 2.

As may be seen from FIG. 3, whereas the control wheel 2 and a portion ofthe carrier plate I immediately above it are disposed horizontally, thedrive wheel 7 is set askew on an axis 8 tilted laterally from thevertical by a small angle. As a matter of practical construction, theportion of the carrier plate to the rear of the control wheel 2 (belowthe control wheel 2 in FIG. 2) have sur faces that are slightly obliqueinstead of horizontal, being parallel to the plane of the disc of thedrive wheel 7 and perpendicular to the axis 8. In this manner theresistance element 20, as is clear from FIG. 3, is mounted in an obliqueplane parallel to the disc of the drive wheel 7. The drive wheel 7 isprovided with an axle 32 molded integrally therewith, held in a hub 33,and is preferably provided with a spring washer, not shown, to preventthe drive wheel from being removed by an axial pull after it is fullyassembled.

The drive wheel 7, as shown more particularly in FIG. 4, is providedwith a crown of peg-like teeth 9 on the side on which the potentiometerwiper 35 is carried. The teeth 9 do not go all the way around theperiphery, being replaced with a continuous ridge 11 for part of theperiphery. The other side of the drive wheel 7 is slightly domed and hasa groove 15 which guides an actuating boss 14 of the pointer 13 that hasa pivot stud at its fulcrum that fits into the bearing 12 of the carrierplate.

The device operates as follows. The control wheel is rotated by theusers thumb acting on the projecting front edge. As it rotates the ridge5, in the form of a single turn spiral near its outer edge, slidesthrough the gap 6 between adjacent teeth 9 of the drive wheel. Becausethe axis of the drive wheel 7 is skewed with respect to the controlwheel 2, the spiral ridge 5 engages the teeth of the drive wheel at onlyone place of its periphery. A complete revolution of the control wheel 2rotates the drive wheel by the angle between successive teeth 9 and thisrotation may be performed in either direction. The ridge l1 acts as astop to limit the range of rotation of the drive wheel to the desiredamount of travel of the wiper 35 on the semicircular portion 21 of theresistance element 20. As the drive wheel rotates,

the boss 14 of the pointer 13 moves in the spiral groove 15, swingingthe pointer 13 across a portion of the disc of the drive wheel 7. Theposition of the nose 16 of the pointer 13 is visible from the front ofthe device where the front edge of the control wheel extends forward ofthe carrier plate 1 and therefore provides an indication of theadjustment of the potentiometer. The control wheel 2 is knurled so thatit may easily be manipulated.

The electrical components of the potentiometer of this invention aremore particularly shown in FIGS. 1, 4 and 5. The resistance element is asemicircular strip of flat material with extended legs having outwardlyjutting tabs 22. The resistance element 20 may consist entirely ofa-resistive composition of the desired characteristics or it may becomposed of a strip of insulation with a film on its upper surfacehaving the desired resistance characteristics. The tabs 22 are providedwith a metallized contact surface as indicated by the dashed shading.This metal surface is preferably of a kind used for contact elementsdesigned for insertion into spring contacts rather than of the kinddesigned to accept solder. The resistance element 20 is seated on asurface of ,the carrier plate 1 which is perpendicular to the axis ofthe hub 23 and its bore 26 in which the shaft 32 of the drive wheel 7revolves. It is not necessary, however, that this slightly obliqueseating surface should extend under the entire lower surface of the tabs22. The line 37, for example, may be the boundary between the obliquesurfaces and the horizontal surfaces of the carrier plate 1. The carrierplate 1 has a raised centering boss 17 the outer edge of which fits theinner edge of the resistance element 20 and provides notches 18 intowhich the inward projections 19 of the resistance element may nest, thusaccurately positioning the resistance element 20 and making it quiteunnecessary to affix the resistance element 20 to the carrier plate 1.The centering boss 17 is interrupted by a channel 38 that provides adeep cavity in the carrier plate through which the lug strip 39 may passunder the resistance element 20 in a position spaced somewhat from theresistance element 20.

The lug 39 has a strip of metal that also has an annular portion 23providing an inner contact surface for the potentiometer wiper 35. Theannular portion 23 of the lug 39 fits around the hub 33. At its otherend the lug 39 is riveted to the carrier plate 1 either by means of ametal rivet 34 or by deforming a boss of the carrier plate projectingthrough the hole in the strip 39. The lug strip 39 continues past therivet 34 to form a projecting end 40 to which a wire may be soldered orcrimped. If desired this lug may also be provided in a form that willmake contact with other circuit elements by being slipped into a springclip.

If desired, the carrier plate 1 may also be provided with a contour tofit the outer edge of the resistance el-' ement 20, or with one or morebosses to engage the outer edge of the resistance element 20.

Construction of the slider or wiper element 35 (in a rotarypotentiometer a potentiometer slider is frequently called a wiper) isshown in FIG. 4. It is made of resilient metal and is held in bosses 42formed integral with the drive wheel 7 which may, if desired, be rivetedover. The semicircular portion 43 rests against the disc of the drivewheel 7. Inner contact springs 44 and 45 extend away from the drivewheel disc for engagement with the annular portion 23 of the lug 39. Theremainder of the structure forms the cusp 46 that,

like the spring portions 44 and 45, extends somewhat away from the discof the drive wheel 7, in this case for making contact with thesemicircular portion 21 of the resistance element 20. A contact stud 47is mounted near the apex of the cusp and this may be a metal or agraphite material chosen for making good contact with relatively littlewear on the resistance element 20. Depending on the size of the contactstud 47 it may be desirable to provide a hole (not shown) in the disc ofthe drive wheel 7 immediately in back of the contact stud The metalcoatings on the tabs 22 may be provided by electroplating, vapordeposition, dipping in molten metal, or by other metallizing processes.Preferably a hard silver plating is provided on these tabs.

FIG. 5 shows a modified form of resistance element for the potentiometerof the present invention. In this case the metallizing of the tabs 22 isconfined to an end portion 52 and there are intermediate parts 53 of theresistance element that add resistanceto the circuit but areinaccessible to the contact 47 of the wiper 35, an arrangement which maybe desired on account of electrical requirements of the particularcircuit into which the potentiometer is placed. At or near the ends ofthe travel of the wiper contact 47 additional metallized portions 54 areprovided, effectively short circuiting small lengths of the resistorelement, so that variations from one device to another in the extent andcentering of the range of travel of the wiper contact 47 will not beaccompanied by any variation in the circuit values for the extremepositions of the wiper.

Although the invention has been described with respect to a particularembodiment, it will be understood that variation and modification arepossible within the inventive concept.

In the preferred construction of the resistance element 20 a carbon filmis vacuum-deposited on a substrate made of cured phenolic resin or someother hard insulating sheet material.

The carbon film is applied before the base resistance element is stampedfromthe insulatingmaterial. The

' hard silvering of the tabs 22 is preferably accomplished by printing.

The wiper 35 is preferably made of suitably plated brass or phosphorbronze, for example silver or tin plated, and the wiper contact 47 ispreferably made of carbon.

The central connection lug is preferably of tinned copper and ispreferably (for simplicity) riveted in place by peening over a studformed integrally with the carrier plate, which is made of glass fiberfortified poly carbonate.

We claim:

1. In a rotary potentiometer having a drive wheel of the peg-toothedcrown gear type, engaged with an approximately one-tum spiral ridgeprovided on'a control wheel in the outer part of a disc surface thereof,said drive wheel and the potentiometer arm being rotatably mountedslightly askew to the control wheel on a carrier plate on which saidcontrol wheel is also rotatably mounted, so that by the engagement ofsaid dontrol wheel and said drive wheel one revolution of said controlwheel will rotate said drive wheel by one tooth, said teeth of saiddrive wheel being in the form of evenly spaced pegs over part of theperiphery of said drive wheel, the improvement which is that theelectrical portion of the rotary potentiometer comprises:

' a resistance element consisting essentially of a substantiallysemicircular segment of an annular disc, including an exposed layer ofresistance material, with the legs thereof extended to form outwardlyextended contact tabs provided with a metallized contact surface, saidresistance element being seated on said carrier plate approximatelyparallel to the disc of said drive wheel with its tabs extendingrespectively beyond opposite edges of said car- I rier plate;

central connection lug means seated on said carrier plate and having anannular disc portion concentric with and within the semicircular segmentof said resistance element and providing an annular contact surface andhaving also a strip portion extending away from said annular portion andat least for part of its length seated in a channel in said carrierplate soas to pass under said semicircular portion of said resistanceelement without contact therewith and providing a connection lug in theneighborhood of its extremity, and wiper means affixed to said drivewheel for making contact with said annular contact surface of saidcentral connection lug means and with said resistance element. 2.Improvement in a rotary potentiometer as defined in claim 1 in whichsaid carrier plate has a raised cenwith positioning notches near thelocation of the said tabs of said resistance element and in which,further, said resistance element has projections fitting into saidnotches, whereby the resistance element is accurately positioned withoutnecessity of affixation.

3. Improvement in a rotary potentiometer as defined in claim 2 in whichfixed resistance portions are provided respectively in series with bothends of the potentiometer by the presence, between the portion of saidtabs having metallized contact surfaces and the ends of saidsemicircular portion of said resistance element, of an extension of saidsemicircular portion not provided with a metallized surface and locatedbeyond the range of movement of theouter contact of said wiper means.

4. Improvement in a rotary potentiometer as defined in claim 3 in whichsaid resistance element has additional metallized surfaces in therespective regions of the ends of the path of travel of said outercontact of said wiper means.

1. In a rotary potentiometer having a drive wheel of the pegtoothedcrown gear type, engaged with an approximately one-turn spiral ridgeprovided on a control wheel in the outer part of a disc surface thereof,said drive wheel and the potentiometer arm being rotatably mountedslightly askew to the control wheel on a carrier plate on which saidcontrol wheel is also rotatably mounted, so that by the engagement ofsaid control wheel and said drive wheel one revolution of said controlwheel will rotate said drive wheel by one tooth, said teeth of saiddrive wheel being in the form of evenly spaced pegs over part of theperiphery of said drive wheel, the improvement which is that theelectrical portion of the rotary potentiometer comprises: a resistanceelement consisting essentially of a substantially semicircular segmentof an annular disc, including an exposed layer of resistance material,with the legs thereof extended to form outwardly extended contact tabsprovided with a metallized contact surface, said resistance elementbeing seated on said carrier plate approximately parallel to the disc ofsaid drive wheel with its tabs extending respectively beyond oppositeedges of said carrier plate; central connection luG means seated on saidcarrier plate and having an annular disc portion concentric with andwithin the semicircular segment of said resistance element and providingan annular contact surface and having also a strip portion extendingaway from said annular portion and at least for part of its lengthseated in a channel in said carrier plate so as to pass under saidsemicircular portion of said resistance element without contacttherewith and providing a connection lug in the neighborhood of itsextremity, and wiper means affixed to said drive wheel for makingcontact with said annular contact surface of said central connection lugmeans and with said resistance element.
 2. Improvement in a rotarypotentiometer as defined in claim 1 in which said carrier plate has araised centering boss on which said annular contact surface of saidcentral lug means is seated, said centering boss being shaped not onlyto provide part of the channel in which the strip portion of saidcentral connection lug means is seated but also being shaped to fit theinner edge of said resistance element and being provided withpositioning notches near the location of the said tabs of saidresistance element and in which, further, said resistance element hasprojections fitting into said notches, whereby the resistance element isaccurately positioned without necessity of affixation.
 3. Improvement ina rotary potentiometer as defined in claim 2 in which fixed resistanceportions are provided respectively in series with both ends of thepotentiometer by the presence, between the portion of said tabs havingmetallized contact surfaces and the ends of said semicircular portion ofsaid resistance element, of an extension of said semicircular portionnot provided with a metallized surface and located beyond the range ofmovement of the outer contact of said wiper means.
 4. Improvement in arotary potentiometer as defined in claim 3 in which said resistanceelement has additional metallized surfaces in the respective regions ofthe ends of the path of travel of said outer contact of said wipermeans.